Cementing plug



J. E. HALL CEMENTING PLUG May 30, 1950 Filed June 21, 19

INVENTOR. dease E. #4

Patented May 30, 1950 UNITED STATES PATENT OFFICE CEMENTING PLUG Application June 21, 1946, Serial No. 678,298

8 Claims.

This invention relates to improvements in a wall cleaning and cementing plug and refers more particularly to a traveling plug used in the cementing operations of an oil or gas Well.

The inventive novelty resides in the construction of the plug and particularly in the structure which provides wall scraping elements distributed over its periphery and permits separate circulation of the well fluids above and below a central plug portion.

In the cementing of an oil and gas well, after the well has been drilled to the desired depth it is often advantageous to introduce cement into the annular space between the casing and the well bore in order to prevent influx of water and gas, and to isolate the producing strata.

To place the cement mix between the casing and well bore it is charged at the wellhead into the casing in a predetermined amount. The quantity of cement supplied is determined by the height to which the cement is to rise in the well bore. To force the cement out of the casing and into the annular space surrounding the casing a plug is inserted into the top of the casing behind the cement charge and is forced downwardly through the casing by pressure of well fluid or mud introduced behind the plug. Near the bottom of the casing the plug is stopped b suitable obstruction such as a shoulder or the casing shoe. When it reaches its destination it has forced the charge of cement out of the bottom of the casing through the casing shoe causing it to rise and fill the well bore to the desired height.

Plugs heretofore used for this purpose have usually been of the piston type constructed either of solid rubber or of wood with disks of resilient material attached to each end, or bands of rubber about the body of the plug. The diameter of the solid rubber plug and the disks or bands of the wooden plug are slightly greater than the inside diameter of the casing, producing a relatively pressure-tight fit.

Numerous difficulties have been encountered where plugs of this type have been used. Among the most objectionable features is the film of cement which is left by plugs of this type on the walls of the casing. This film, after setting, produces scale which is objectionable throughout the life of the well, particularly to producing equipment. A further hardship often encountered is the fact that as the plug moves downwardly in its travel it extracts fluid from the cement mix causing a concentration of relatively dry cement to build up in front of the plug. This efiect in certain instances has been known to lodge the as 2 plug permanently in the casing and prevent its travel to its ultimate destination. If the plu is not driven to the bottom of the casing a charge of cement remains in the casing below" the plug and an inadequate amount of cement mix is charged into the well bore. Thus the cement is improperly placed and the cementing job hecomes wholly ineffective.

An object, then, of the present invention is to provide a plug by which agitation and mixture of the cement is constantly kept up in front of the plug during its downward travel. Likewise, behind the plug the fluid mud is continuously circulated from a central compartment through the plug wall to be intimately intermingled with any cement film which may have passed the plug and which is plowed up from the surface of the inner wall of the casing by abrading elements.

A further object of the plug construction is to prevent loss of fluid from the mixture in front of the plug by local circulation set up through the plug wall as the plug advances. In other words, the viscosity of the fluid in front of the plug is kept relatively constant.

Other and further objects will appear from the following description.

In the accompanying drawings which form a part of the instant specification and are to be read in conjunction therewith, and in which like reference numerals indicate like parts in the various views,

Fig. 1 is a side view of a plug embodying the invention,

Fig. 2 is a central vertical section taken along the line 2--2 in Fig. 3 in the direction of the arrows, and

Fig. 3 is a view taken along the line 3-3 in Fig. 2 in the direction of the arrows.

Referring to the drawings, the wall cleaning plug consists of a body portion designated as a whole by the numeral i0. Centrally of the body is a cylindrical portion Ilia having a diameter which fits snugly Within the well casing i l. Above the cylindrical portion is an upper hollow circulating tube illb enclosing an upper cylindrical chamber l2. Upon the outer periphery of the upper tube Illb arranged at different heights and staggered circumferentially about the tube surface are a plurality of diamond shaped abrading plows l3. Since the outside diameter of the upper circulating tube is somewhat smaller than the cylindrical portion Ilia, an annular shoulder is formed at the base of the tube. The diameter through the tube, including the plows, is slightly greater than the diameter of the cylindrical por- J) tion Elia. The upper circulating tube including the plows has a somewhat greater diameter than the cylindrical portion causing the plows to scrape or abrade the inner surface of the casing during the plug travel.

In the wall of the upper circulating tube adjacent the shoulder where it joins with the cylindrical portion [ta are a plurality of circumferentially arranged ports M. Below the cylindrical portion lea is a similar hollow circulating tube IEO. This tube, like the upper tube, has scraping elements It of rectangular shape. Beneath each of the scrapers are ports It which communicate with the hollow central chamber ll of the circulating tube and permit the passage of fluid from the outer periphery of the lower circulating tube into its hollow interior. The lower surfaces of these scrapers are preferably inclined upwardly to facilitate fluid flow from the scraping edges into the ports [6.

Describing the operation of the plug, after the cement has been introduced at the casing head the 'plug is inserted. Ihe cementing head into which the plug enters may be slightly enlarged to permit its easy admittance. After the plug is inserted, the cementing head is closed and pressure is imposed behind the plug by pumping mud fluid into the casing under sufficient pie"- sure to move the plug downwardly. The plug then acts as a piston between the cement mix and mud fluid and during its travel forces the cement mix downwardly and out through the bottom or" the casing into the annular space between the casing and well bore.

During its downward travel the cement mix in front of the plug and adhering to the casing wall is circulated through ports it in the wall of the lower circulating tube by the action of scrapers i5 and is discharged into the central portion or the casing. Scrapers it not only create circulation of the mix from the annular space between the casing and circulating tube through ports it, but maintain a relatively clean surface ahead of the plug due to their scraping action.

The cylindrical portion i la fitting snugly within the casing acts as a piston separating the cement mix and mud fluid, forcing the cement mix ahead of the plug and preventing intermingling of the two fluids. Any film of cement adhering to the inner surface of the casing which passes the cylindrical portion of the plug will be disintegrated by members These diamond shaped elements around the upper tube fit tightly against the casing and plow furrows through any film that may be formed. Removal of the film by members It also causes the cement ml to be disseminated through the mud body surrounding the upper circulating tube. The proportion of mud and cement behind the plug is such that the cement becomes a part of the mud fluid and is prevented from setting.

l-lereinbefore circulation of the mud through the upper circulating tube has been described. This circulation is downwardly through the corn tral hollow chamber l2 and out through the lower ports I l located immediately above shoulder formed by the cylindrical portion lea. Contact between the inner surface of the casing and plow members i3 during the plugs travel ca s an upward movement of the mud at the inner casing surface. Also frictional contact between the outer periphery of the mud column w the inner surface of the casing will retard t e favel of the mud fluid at the inner caring surface whi t will draw fluid from the center oi the column through the ports.

Circulation of the mud and cement fluids above and elow the plug during its travel reduce the possibility of accumulation of cement and mud on the inner casing surfaceby'remixing partially set fluids adhering to the inner surface of the casing.

Thus it will be seen that the objects of the invention have been accomplished. There has been provided a wall cleaning plug particularly adapted for use in cementing oil wells for remove ing solid and film accumulations on the inside surface of the casing. It will be appreciated that the plug is adapted as well for cleaning pipe lines or removing solid accumulations from pipes of any kind through which fluid is moved.

As suggested, the novelty resides primarily in the construction of the plug comprising a central cylindrical piston portion, upper and lower circulating tubes having abradin'g elements for disruptionof the film or accumulations onthe inner surface or the pipe. 7

It will be understood that certain 'featuresand subcoinbinations are of utility and-may be employed without reference to other features and subc'ombinations. This is contemplated by and is within the scope of'theclaims. ltshould be obvious that various changes may be made in the details of the plug construction within the scope of the claims without departing fro-n1 the spirit of the invention. It is, therefore, understood that the invention is not limited to the specific details shown-and described.

Having thus described my invention, I claim:

1. A cementing plug having a central cylindri cal section with an outside diameter at least that of-the inside diameter of the casing in which the plug is to'be run, a pair of open ended circulating tubes smaller in diameter than the inside diameter of the casing, said tubes connected respectively to the top and bottom of the central cylindrical section and having circulating ports through their peripheral walls, and casing wall scraping members distributed uponthe' exterior walls of the respective to es, in circumferentially spaced relationship.

2. "A cementing plug as in claim 1 in which the scraping members on the upper tube constitute a plurality oi plow shaped elements raised in relief sufilciently above the tube surface to contact the inner casing wall and arranged in staggered relationship circumferentially about the tube, the. circulating ports positioned adjacent the top or" the central cylindrical section.

3. A cementing plug as in claim 1 in which the scraping members on the lower tube are raised in relief sufficiently above the tube surface to contact the inner casing wall and arrangedin staggered relationship circumferentially about the tube, the circulating ports in the lower tube positioned beneath the scraping members.

'4; A cementing'plug as in claim 1 in which the scraping members on the lower tube are raised in relief sufficiently above the tube surface to contact the inner casing wall and arranged in staggered relationship circumferentially about the tube, the lower surfaces of said members inclined upwardly from front to rear and the circulating ports positioned beneath the scraping members.

5. A cementing-plug comprising a central section at least as large in diameter as the" inside 7 diameter of the casing'to'be run, with smaller 'cndse'ctions projecting forwardly and rearwardly from said central section, a plurality of lugs on each end section adapted to engage the inside wall of the casing, said lugs arranged in circumferential rows, the lugs in each row being spaced circumferentially from one another and the lugs in adjacent rows being staggered relative one another.

6. A cementing plug comprising a central section at least as large in diameter as the inside diameter of the casing to be run, with smaller end sections projecting forwardly and rearwardly from said central section, a plurality of lugs on each end section adapted to engage the inside wall of the casing, said lugs arranged in circumferential rows, the lugs in each row being spaced circumferentially from one another and the lugs in adjacent rows being staggered relative one another, the forward section of the plug having a hollow bore, substantially radial ducts through the forward section connecting the bore thereof with the space outside of the plug, each duct disposed forwardly of one of the lugs.

7. A cementing plu comprising a solid cen' tral section at least as large in diameter as the inside diameter of the casing to be run with smaller end sections projecting forwardly and rearwardly from said central section, a plurality of circumferentially spaced scraping lugs on each 6 end section adapted to engage the inside wall of the casing, the forward section of the plug having a hollow bore, substantially radial ducts through the forward section connecting the bore thereof with the space outside the plug, each duct disposed forwardly of one of the lugs.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,989,035 Blum Jan. 22, 1935 1,994,072 Hardcastle Mar. 112, 1935 2,167,778 Robinson Aug. 1, 1939 2,175,770 Dodson Oct. 10, 1939 

